Superheterodyne receiver



Sept. 16, 1952 J. ARENDS SUPERHETERODYNE RECEIVER Filed 001;. 7. 1949 LOW FREQUENCY AMPLIFIER DEMODULATOR TANDARD OSCILLATOR ea 5v v INVENTOR. ,JACOBUS LUDOVICUS ARENDS' ',,L 7 AGEN Patented Sept. 16, 1952 SUPERHETERODYNE RECEIVER J acobus Ludovicus Arends, Hilversum, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn, trustee Application ct0ber.7, 1949,,Serial No. 120,143 In the Netherlands October 8, 1948 This invention relates to superheterodyne re-v ceivers having automaticfrequency correction of the local oscillator and may be applied with particular advantages to receivers intended for the reception of single side-band signals having a pilot frequency modulation component.

In superheterodyne receivers for automatic frequency correction, it is known to connect an amplifying tube, operating as a variable reactance, parallel to the frequency-determining circuit of a local oscillator, said amplifying tube having supplied to it, as an AFC voltage, a control voltage derived from a frequency'detector connected, for example, to'the intermediate-fre quency amplifien: V 1

Such an AFC arrangement has the advantages of rapid control, high electrical sensitivity and low sensitivity to mechanical vibration, but has the disadvantage of a socalled back setting force" of frequency drift that is to say, the frequency tends to return to the uncorrected value when the control voltage is lost due, for example, to fading of the incoming signal. Furthermore; such arrangements in practice permit "of covering only a very limited control range. It is furthermore known for AFC purposes to control the sense of rotation of an electric motor which adjust the value of an impedance connected parallel to the frequency-determining circuit of the oscillator according to the polarity of the control voltage. An advantage of such a mechanical control is the absence of the drift referred to, since the motor'stops as soon as the required frequency correction is carried out and remains at rest when the control voltage islost', so that the corrected frequency remains at the value to which it was last adjusted. A further advantage is the comparatively large'control range that may be obtained. However, this controlis subject to mechanical inertia and hence is slow inaction, and also the electrical sensitivity Blow. The combined use of the two above-described control systems results in an AFC circuit which provided an advantageous compromise with regard to speed of control, control sensitivity, control range, absence of the said drift and insensitivity to mechanical vibration. I According to the present invention a superheterodyne receiver-comprises a grid-controlled mixing-tube and a. local oscillator having a back coupled grid-controlled electronic tube, of which at least the control gridan'dthe anode do not form part of the mixing-tube system and in which the local oscillator signal and the incoming signal are supplied to the mixing tube and the in- 6 Claims. (Cl. 25020) termediate-frequency oscillations derived therefrom control an intermediate-frequency amplifier, this receiver comprising simple means by which'the local oscillator is automatically'corrected in frequency with the use of a direct AFC control voltage derived from a frequency detector connected to the intermediate-frequency amplifier. I The AFC voltage is supplied to a control grid of the mixing tube system'which operates as a direct-voltage amplifier for the AFC voltage, whilst the'anocle circuits of the mixing and oscillator tube systems, which are otherwise separated, include a common direct-currentresistance across which appears the amplified: AFC voltage supplied to the oscillator anode for the purpose of frequency correction. I

The use-of" the mixing tube system'as a directvoltag'e amplifier for the AFC voltageresults in a comparatively high sensitivity with a reasonable control range, whilst disturbing couplings may beavoided in a very simple manner, viz by shunting the common ohmic resistance for high-frequency, intermediate-frequency and oscillator frequency by means of a condenser.

*The variation in-the direct current position of the mixing tube system produced as a result of the AFC control voltage supplied to a control gridof the mixingtube system may give rise to unwanted variation in the conversion slope of the mixing tube system and to distortion.

According to one form of the invention these difliculties are obviated by coupling the frequency-determining circuit of the oscillator to a frequency corrector which preferably operates without the said drift and which compris'esa control member which is "moved mechanically (and hence comparatively slowly) upon occurrence of an AFC voltage. r

' It is thus ensured that frequency corrections occurring may give rise to unwanted variation in the conversionslope of the mixing tube system and to distortionfor a short-period only, since the frequency'correction of theimmediately operating electronic control will be gradually taken over by the-mechanical frequency corrector until the electronic frequency corrector is fully released and hence unwanted variation in the direct-current position of the mixing tube system no longer occurs. I I

In order that the invention may be readily carried into effect, one example will now be described more fully by reference to the accompanying drawing, which shows a superheterodyne receiver siiltsablefor the reception of single side-band sign The single side-band signal with suppressed carrier wave is received by an aerial l and is assumed to comprise a 10 kc./sec. pilot frequency in addition to the intelligence signals. The pilot frequency constitutes a modulation component which may lie either within or without the frequency band constituted by the intelligence sig:

nals. This signal is supplied, after amplification.

in a high-frequency amplifier 2, together with the oscillator signal from a first crystal-controlled local oscillator 3, to a first mixing stage 4.

The intermediate-frequency signal of 590 to 496. kc./sec. obtained after mixing contains the frequency of 500 kc./sec. which representsthe 10 kc./sec. pilot frequency modulation component. This I. F. signal is amplified in an intermediatefrequency amplifier 5 and the output is supplied";

through a grid condenser 6 and a leak resistance 1 to a first control grid 8 of a hexode 9 serving as a mixing tube. The local oscillator which is automatically corrected in' frequency has a triode.

I with anode resistance 28, which ,tri'od may, if desired, be incorporated together with the hexode 9 in one bulb and the anode circuit of which furthermore includes the oscillatory circuit. determining the oscillatory frequency and constituted by a condenser H and an inductance [2.

a feed-back coil [3 included in the grid circuit of the triode I 0 and supplied through a grid condenser l4 .and a leak resistance I5 to the control grid of triode ID, which control grid is coupledvia a condenser Hi to a third grid ll of the hexode 9. The single side-band signal produced in the anode circuit of the hexode and extending, after the twofold transposition to which it has been subjected, through a range of frequencies of to 6 kc./sec. in this example, is supplied for the purpose of separating the intelligence signals-and the pilot frequency to a demodulator l8 through a-cut-ofi stage I9 and to an amplifying tube through a band-pass filter 2! included in the anode circuit of the hexode 9. I

A local oscillator signal originating from. a standard oscillator 22 having a 10 kc./sec. crystal is supplied to the demodulator I8 and the low.- frequency signals (0 to 4 kc./sec.) produced in the output circuit of the demodulator; are supplied through a low-pass filter 23 and a lowfrequency amplifier 24 to a reproducing device 25 which is connected thereto. I The band-pass filter 2| included in the anode circuit of the hexode 9 comprises a first parallel,

circuit including a condenser 26 and an inductance 27. That extremity of this parallel circuit which is remote from the anode of the hexode is comiected through a resistance 41 to theanode lead, the other end of the parallel circuit being connected through a condenser 29 to one end of a second parallel circuit comprising a condenser 38 and an inductance 3| andthrough a lead 32 to the control grid of the amplifying tube 20.

The other end of the second parallel circuit is connected to earth, The pilot signal passed by the band-pass filter 2i and amplified in the anode circuit of the amplifying tube 20 is supplied byway of a blockingcondenser 33 and a seriesresistance 34 to a bilateral limiter formed by two rectifiers 36 and 31 connected in parallel opposi tion and included in the control-grid circuit of an amplifying tube 35.

The pilot signal thus limited is selected, after having been amplified in the. anode circuit of amplifying tube 35, by a tuned circuit comprising a coil 38 and a condenser 39, whereuponthe:

The oscillations generated are back-coupled through pilot signal is supplied by way of a coupling condenser 40 and an output resistance 4| to a frequency detector 42 in order to be compared with the comparative signal produced by the standard oscillator 22.

The frequency detector 42 supplies a control voltagewhich corresponds-W0 the polarity and value of the frequency orfiphasefdilference between pilot frequency and comparative signal and which is developed at push-pull output resistances 43 and 44. Frequency detector 42 may be constituted by any of a variety of known mixing detector circuits. A suitable circuit is shown,

' forexample, in anarticle by L. I. Farren in Wireless Engineer, vol. 23 (1946), pages 330 to 340 and in particular Fig. 6 thereof. The output resistance is constructed as a potentiometer and the AFC control voltage which appears at a sliding contact 45 is supplied by way of a resistance 46 to the third grid ll of the mixing hexode 9 which operates as a direct-voltageamplifier 'for the control voltage.

By connecting'those ends of'the output an: pedances Hand 28 of the mixing hexode 9 and the oscillatorftriode it which are remote from the anodes of the said tubes through a common.

ohmic resistance 41 to the positive terminal of the anode voltage supply, the variation in anode voltage produced in the. anode circuit of the hexode due 'to.a variation in the control voltage at the thirdgrid ll results in a variation in the anode voltage'of the oscillator and hence a variation the frequency of the local oscillator. In

order to avoid disturbing couplings,'the common.

resistance '41 is short-circuite d for oscillator and intermediate-frequency oscillations by means of a condenser 48.

' The, positive or negative control voltage set up at the output re'sistances'43 and 44 'of the frequency detector 42 is supplied through resistances 49 and 50 respectively to the control grids of two, push-pull amplifying tubes 5!, 52, both of which, are just cut-off in theabsence of a direct control- According to the polarity of the AFC.

connected throu he lead 59 to the earthed end, and, through a trimmer condenser 6i included in a lead-BO, to the'other end of the frequency:;,

determining oscillatory circuit ,l I, I 2 of the, local oscillatortriodelfl. Y 3

,Upon the occurrence of a maintained frequency variation of theincoming signal, the AFC; control voltage appearing atthe sliding contact; 45 in the output circuit of the frequency'detec-v tor 42 results in a variation in the biasing poten-g tial-;of the third gridH of the mixing hexode and,;- .as previously explained, bring about acorn rection of the local oscillator frequency-.. How:- ever, this variation in the direct-current position of the mixing tube also gives rise to unwanted. variation in the conversion slope, of the mixing? tube and hence to distortion of theincomingsig-t The disadvantages referred :to which 8.1365111? herent in they above described jelectroni'c control are minimised by iprovidingrin addition topthe,

particularly simple and inertialesselectronic con-. trol described, a mechanical and slowly acting frequency correction ofthe local oscillatorfrequency, so that the duration of distortionyand the-like is limited .to the; period of operation of the. mechanical control. The --mechanical control gradually takes over the frequencycorrection of theelectronic control until the latter. is released almost completely, thereby eliminating the'initial. variation in the direct-currentposition of. the mixingqtubeg.

What I'claim isz. 1,. A superheterodyne receiver circuit arrange.- ment; comprising a first electron discharge system having input and output circuit means, means to apply a received signal waveto the in-.;. put circuit means of said first discharge system, a second electron dischargesystem having. input and output circuit means, a resistance element interposedin both the output circuit: means .of

intercoupling the output and input .circuit'means of .said second discharge system in regenerative relationship to produce a source oflocal .oscil'- lation, said source undergoing changes in the frequency thereof proportional 'to changes in po-' tential applied to the .said output circuit means thereof, means to applysaidv local oscillation to.

the;input..circuit means-or said first discharge system to mix said received-signal wavewand said localz oscillation thereby 'to produce in the output circuit means of saidfirst discharge:sys:-.

tem an intermediate. frequency. wave having-a given frequency, a detector :stage responsive. to

said intermediate frequency. wave coupled to saidoutput-circuit means of said firstelectron discharge system, means to derive from said.detecfied' control voltage and to thereby apply'said amplified control voltage to thexoutput circuit means of saidsecondidischargesystem to vary the frequency of saidsource in a direction suppressing said variations in frequency of said intermediate frequency wave from said given frequency.

2. A superheterodyne receiver circuit arrangement, comprising a first electron discharge system having a cathode element, first and second control grids and an anodeymeans. to apply-a received signal wave to one of the control grids of said first discharge system, a second electron discharge system having a cathode element, a controlgrid and an anode, first and second cut put circuits each coupled to-a respective; one of said anodes, a resistance element interposdjin both said output circuits, means'intercoupling the anode and controlgridiof said second discharge system in regenerative relationship to produce a source of local oscillation. said source undergoing changes in the frequency thereof proportional to changes in. potential applied to the anode of said second discharge system, means to apply said local oscillation to the other control grid of said first discharge system to mix said received signal wave and said local oscillation thereby to produce in the output circuit coupled to the anode of said first discharge system an interme diate frequency wave having, a given fre--.; quency, av detector sta'geresponsive to said intermediate frequency wave coupled to said ;out-- putscircuit coupled to the anode of said'first. eleo-i" tron discharge] system, means to derive from said detector stage a'direct control voltage proportional; to variations infrequency-of'said inter-- mediate. frequency wave from said given -frequency, means to apply said control voltageto one. of thez-controlgrids of :said first discharge system .t05produce across said resistance element anLamplifiedcontrol voltage and to thereby; apply saidamplified. control voltage to :the anode; of said. second 1 discharge system to vary; the sire;- quency :of said source in. a direction suppressing said. variations in frequencyof said'interm'edlate frequencywav from said given frequency.'"-;.-..

3. A :superheterodyne receiver circuit arrange-- ment, comprising. a first electron discharge systemqhaving. .acathode element, first and second. control. grids and ran anode, means to ,apply a, receivedsignal wave to one of the'controlgrids: of said first discharge system,.a. second electron: discharge system having acat-hode element; a'. controlgrid and an anode,; first andsecond out'-' putimpedance elements each havingone. end thereof coupled to a respective one of said .-an-.- odes, a resistance element intercoupling the'otherends-of said impedance elements and; asource: of operating; potential, means intercoupling. the; anode and control grid of said second-discharge.

systemin, regenerative, relationship to producea source, of local I oscillation, said source undergoe; ing changes in the frequency thereof proportion-*- al to changes in potentialappliedtotheanode of said seconddischarge system, means tolapply said localoscillation to the other control gridzof; said first discharge system to mix said received signal wave and said local oscillation. thereby to produce in the (output circuit coupled to the an ode of; said firstdischargesystem an intermediate; frequency wave having a given frequency; a'dee tectorv stage responsive. to said intermediate frequency wave coupled-to said output .circuit;cou'-.. pled to the anode of said .firstelectron discharge system-,means to derive, from said detector stage a.dir ect.control voltage proportional. to varia-' tions in frequency of said intermediate frequency: wave from said given frequency, means to apply. said. control voltage to one ofthe control grids of said first-discharge systemto produce ..acro'ss said'resistance element. an amplified control volt;- age-:'and to thereby apply. said amplified control voltage .tothe anode of said second discharge system to vary thefrequency of said source in' a direction suppressing said variations in frequency: of said intermediate frequencywave frompsaid' givenfrequency. r Y 2 4; A superheterodyner receiverficircuit arranger-1 ment, comprising a first electron discharge system having a cathode element, first and secondcontroligrids and an anodeJneans to apply -a' receivedsigna'l wave to said first control grid-oi saidfirst discharge system, a'second ele'ctron discharge system havingv a cathode element, a con'--- trol grid-and an anode, eachof Saiddischarge systems being included in the same envelope, first and second output circuits each coupled to a respective one of said anodes, a resistance element interposed in both said output circuits, means intercoupling the anode and control grid of said second discharge system in regenerative relationship to produce a source of local oscillation, said source undergoing changes in the frequency thereof proportional to changes in potential aptectorstagemeans toderive from said frequency detector stage a direct control voltage proportional-to variations in frequency of said intermediate-:frequencyrwave' from said given frequency,a=means:tozapply said control voltage to said second control grid of said first discharge systemto produce across said resistance element an amplified control voltage and to thereby apply saidl'amplified control voltage to the anode of said second discharge system to vary the frequency of said source in a direction suppressing said .variations in frequency of said intermediate frequency waveifrom saidgiven frequency.

. .5: Alsuperheterodyne receiver circuit arrangement. comprising a first electron discharge system having input and output circuit means, means-to apply a received signal wave to the input circuit means of said first discharge system, a second electron discharge system having input andoutput' circuit means a resistance element interposed in vboth the output circuit means of said-first and second discharge systems, means intercoupling the output and input circuit means of. said second discharge system in regenerative relationship to produce a source of local oscillation; said output circuit means of said second discharge system comprisinga frequency determining circuit having a variable reactance element, saidlsource undergoing changes in the frequency thereof. proportional to changes in potential applied to the said output circuit means of said second discharge system, means to apply said local oscillation to the input circuit means of said first dischargesystem to mix said received signal wave and said local oscillation thereby to produce .in thezoutput circuitimeans of said-first discharge system an intermediate frequency wave havin a given frequency, a detector stage responsive to said intermediate frequency wave coupled to said output circuit means of saidfirst electron "discharge-system means to derive from said detectorstage a direct control voltage proportional to. variations in frequency of saidintermediate. frequency wave from said given frequency, means to apply said control voltage to the input circuit means of said first discharge systemto produce across said resistance element an amplified controlzvoltage and to thereby apply said amplified control voltage to the output circuit means of saidsecond discharge system to vary the frequency of said source in a direction suppressing said variations in frequency of said intermediate frequency. wave from said given frequency, a mechanical-control member responsive to an ap lied potential, means to apply said control voltage tosaid control member, and means vto intercoupl'e said control memb'er and said variable reactance element to vary the reactance of said variable reactance element upon variations in said control voltage thereby to vary the frequency of said source in a direction further suppressing said variations in frequency of said intermediate frequency wavefrom said given frequency.

:65 A superheterodyne receiver circuit arrangement, comprising-:91 first electron discharge system having input and out ut circuit means, means to apply areceived signal wave comprising a single side band signal having a' pilot frequency modulation component to the input circuit means-of said'first discharge system, a second electron discharge systemhaving input and output circuit means, a resistance element interposed in both the-output circuit means of said first and second discharge systems, means intercoupling the output and input circuit mean of said second discharge system in regenerative relationship to produce a source of local oscillation, saidisource undergoing changes in the frequency thereof proportional to changes in potentiality plied'to the said output circuit means thereof,

means to apply said local oscillation to the input circuit means of said'firstl discharge system to mix said received signal'wave and said local os-' cillation therebyto produce in the output circuit means of said firstdis'char'ge system an intermediate frequency wave having a given central frequencyand a given intermediate frequency modulation component corresponding to said pilot frequencycomponentfla frequency detector stage responsive to said intermediate frequency wave coupled to said output circuit means of said first electron discharge system, means to derive from said frequency detector a-direct control voltage proportional to variations in frequency of said intermediate frequency modulation component from said given intermediate frequency modulation component; means to apply said control voltage to theinput circuit of said first discharge system to produce across said resistance element an amplified control voltage and to thereby apply said amplified control voltage to the output circuit of said second discharge system'to vary the frequency of said-source in a direction suppressingsaid'variations in frequency of said intermediate frequency ,modulation component from said given intermediate frequency modulation component.

JACOBUS LUDOVICUS ARENDS,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Crosby ..r- July 4, 1950 

